Abstract
(1) Seasonal change in the amount of deposition and the chemical nature of the deposits have been investigated in Nakanuma, a swamp it Ibaragi Prefecture.
(2) Seven glass bottles were suspended from a buoy at the depth of 1-10m above the deepest bottom of the lake. At intervals of about one month, they were hauled up, and their contents examined.
(3) The rate of deposition was largest between March. 11 and April 29 (14.8g/m2/24hours), and it was smallest between July 11 and August 25 (7.8g/m2/24hours).
(4) The percentage of total nitrogen was found to vary between the two extreme value of 0.62% (Mar. 11-Apr. 29) and 1.05% (Jun 24-July 17). The content of organic carbon varied between 4.7 (Mar. 11-Apr. 29) and 6.6% (Aug. 25-Sept. 24). While, the surface layer of the bottom deposits, which was dredged from the deepest part of the swamp, contained 0.38% of total nitrogen and 3.3% of organic carbon.
(5) The deposits, formed during the summer stagnating period, contained large amount of organic detritus, which were produced as the result of biological production in the lake. On the other hand, the deposits, during the winter and early spring, contained great quantities of inorganic remains which were brought from the shore or bottom of the swamp by the wind action or water circulation.
(6) The value of the ratio N/C was larger during the spring and summer (0.13-0.19), and smaller during the autumn and winter (0.11-0.12). While, the bottom deposits showed 0.11 as N/G ratio.
.The abnormal value of N/C ratio during June and July (0.19) was explained as the result of the appearence of large amount of blue algae (N/C, 0.17-0.19) in this period.
(7) As compared with other lakes, it seemed possible to suppose the correlation between to suppose the corre-lation between the quantity of the deposition and the dean depth of lakes.
